Most drinking (potable) water distribution reservoirs are designed to fill and draw out from the bottom. This means that without mixing, the last water entering the reservoir is usually the first water to flow out. The stratification that occurs due to this design creates several water quality issues with regard to disinfectant levels and disinfection byproducts. Weather related temperature changes or a dramatic difference between the source water temperature and the ambient temperature of the tank may also cause stratification. Colder water is denser and negatively buoyant and therefore stays in the lowest portion of the tank. To help improve water quality and to meet regulatory requirements, mixing systems are typically used. Current mixing systems utilize draft tubes, air bubbling, duckbill, or mechanical (screw) type mixers.
A difference in temperature of inlet water and tank water can allow stratification to occur. Stratification can occur year round, but is most problematic during warm season months. The colder inlet water is denser, negatively buoyant and therefore stays in the lowest portion of the tank. Without a mixing system, each additional fill and draw cycle will continually increase the water age in the top part of the tank. This allows water quality problems to develop such as a loss of disinfectant residual, increase in total trihalomethanes (TTHM), and bacteria regrowth.
There is a need for an improved potable water mixing system for achieving complete mixing to yield a homogenous solution throughout the tank water volume and eliminating any thermal, chemical, and microbiological stratification, thereby preserving water quality.
There is also a need for a potable water mixing system that can be used in a number of below ground and/or elevated water storage tanks of varying sizes and dimensions.